Cast iron alloy

Abstract

The invention proposes a cast iron alloy for cast iron products which are highly thermally stable, the alloy containing, as nonferrous constituents, at least the elements C, Si, Mo, Al and, as admixtures, Ni, Mg and/or S, and the C content being less than 2.9% by weight. The alloy is used, for example, to produce exhaust manifolds or turbocharger casings.

1. A cast iron alloy for a cast iron product characterized by high thermal stability, the alloy consisting essentially of, as nonferrous
 constituents, positive additions of C, Si, Mo, Al, Ni, Mg, Zr, wherein C is present in an amount of less than 2.5to 2.8% by weight, the Si content is 4.7 to 5.2% by weight, the Mo content is 0.5 to 0.9% by weight, the Al content is 0.5 to 0.9% by weight, the Ni content is 0.1 to 1.0% by weight, the Mg content is up to 0.05% by weight and 
 wherein the Zr content is 0.1 to 0.4% by weight, wherein graphite in the as cast iron alloy comprises spheroidal graphite. 
 
     
     
       2. A cast iron alloy as claimed in  claim 1 , including S up to 0.05 wt. % max, and balance essentially Fe. 
     
     
       3. The cast iron alloy as claimed in  claim 1 , wherein the cast iron product comes into contact with exhaust gas from an internal combustion engine. 
     
     
       4. The cast iron alloy as claimed in  claim 1 , wherein the cast iron product is an exhaust manifold for
 receiving exhaust gases from an internal combustion engine. 
 
     
     
       5. A cast iron alloy according to  claim 1 , wherein S is less than 0.01. 
     
     
       6. In combination, an internal combustion engine and a cast iron product comprising an exhaust manifold for the internal combination engine, the cast exhaust manifold being contacted with exhaust gases from the internal combustion engine, the cast exhaust manifold comprises a cast iron alloy consisting essentially of, as nonferrous constituents, positive additions of C, Si, Mo, Al, Ni, Mg, Zr, wherein C is present in an amount of 2.5 to 2.8% by weight, the Si content is 4.7 to 5.2% by weight, the Mo content is 0.5 to 0.9% by weight, the Al content is 0.5 to 0.9% by weight, the Ni content is 0.1 to 1.0% by weight, the Mg content is up to 0.05% by weight and wherein the Zr content is 0.1 to 0.4% by weight, wherein graphite in the as cast iron alloy comprises spheroidal graphite, wherein the exhaust manifold is exposed to temperatures of greater than 900° C. 
     
     
       7. A cast iron alloy according to  claim 6 , wherein S is less than 0.01. 
     
     
       8. A process for producing the cast iron alloy as claimed in any one of  claims 1 ,  4  and  6 , wherein the Al and Zr are added as an Al—Zr prealloy immediately before the alloy melt is cast. 
     
     
       9. A process for producing the cast iron alloy as set forth in  claim 8 , wherein the temperature of the alloy melt is over 1460° C. immediately prior to casting.